1. Field of the Invention
The present invention relates to a storage battery such as a nickel-hydrogen storage battery, a lithium-ion storage battery, a nickel-cadmium storage battery, a lead storage battery or the like, and more particularly to an assembled storage battery unit of the collective type composed of a plurality of storage batteries integrally assembled as a unit.
2. Description of the Prior Art
In recent years, development of a high performance storage battery has been required by rapid popularization of portable equipment. Under the circumstances, a sealed type alkaline storage battery superior in charge-discharge characteristics, reliability and ease of maintenance has been used as an electric power source for various kinds of portable equipment. In the sealed type storage battery, oxygen gas generated from the positive electrode in the occurrence of overcharge is absorbed by reaction with the negative electrode for maintaining the battery casing in a sealed condition. The reaction heat caused by absorption of the oxygen gas results in rise of the battery temperature. The rise of the battery temperature does not cause any problem in a small size cylindrical or parallelepiped storage battery of less than 2 Ah currently used.
However, development of a storage battery of large capacity for use in electric automotive vehicles is required in recent years. Such a storage battery of large capacity is provided in the form of an assembled storage battery unit of the collective type composed of a plurality of alkaline storage batteries integrally assembled as a unit. In the storage battery unit of the collective type, sufficient radiation of heat from the batteries is deteriorated due to an increase of the amount of heat generated at charging, and the discharge capacity of the battery unit is therefore decreased, because of the rise in battery temperature caused by accumulation of the now-dissipated heat. In addition, the charge-discharge characteristics of storage batteries located at the opposite sides and central portion of the battery unit become irregular due to a difference in temperature.
In Japanese Patent Laid-open Publication No. 7-235326, there has been proposed an assembled alkaline storage battery unit of the sealed type wherein ventilation spaces are formed among a plurality of storage batteries located adjacent to one another. In the alkaline storage battery unit, each battery casing made of synthetic resin is formed at tis outer surface with a plurality of equally spaced parallel vertical ribs which are retained in contact with the corresponding parallel vertical ribs formed on an adjacent battery casing to form the ventilation spaces. The ventilation spaces are useful to exhaust the heat generated in the battery unit to the exterior therethrough for cooling the storage batteries respectively. This is effective to prevent the occurrence of a difference in temperature among the storage batteries located at the opposite sides and central portion of the battery unit thereby to make more uniform the charge-discharge characteristics of the storage batteries.
In the sealed type alkaline storage battery unit described above, the vertical ribs located at the opposite sides of each storage battery are formed at their upper portions with a projection and a recess respectively and at their lower portions with a recess and a projection respectively. When the storage batteries are assembled as a unit, the projection and recess of the ribs are coupled with the corresponding recess and projection formed on the ribs of the adjacent storage battery for positioning the storage batteries in place. However, engagement of the storage batteries at their ribs positioned in place does not serve to enhance the mechanical strength of the assembled storage battery unit. For this reason, reinforcement members are used for assembly of the storage batteries to enhance the mechanical strength of the assembled storage battery unit. As a result, the manufacturing cost of the storage battery unit is increased, and the assembly process of the storage batteries becomes complicated. In the case that the assembled storage battery unit is used in an electric automotive vehicle, connecting members for connecting the terminals of the storage batteries to one another are disconnected from the terminals if the assembled cells are displaced due to vibration of the vehicle. In addition, it is difficult to effect removal of gas at the recesses in the ribs during molding of the battery casings.